This invention relates to moisture sealing of electronic devices and, more particularly, to coating a capacitor element with a moisture resistant material layer.
Aircraft and other equipment utilize capacitors in avionics, power converters, electric/electronic motor controllers and other applications. Capacitors are used for electrical energy storage, waveform shaping, electromagnetic interference, lightning protection and other similar functions. Increased use of electronic devices in avionics and other applications, such as in electronic motor controllers in place of previously used hydraulic, pneumatic, or other power sources, increases the number and size of capacitors used in these applications.
Aircraft and other equipment that are exposed to ambient unprotected weather conditions and/or to high humidity environments in normal operation or storage require that exposure to moisture not affect the operation, life, maintenance cost, or reliability of associated electronic equipment.
Certain equipment that utilizes capacitors, as an example aircraft, perform their intended functions more successfully if size and weight are minimized. Many capacitive elements, such as those constructed of wound elements of metallized polymer film, will degrade and fail due to corrosion or other moisture-related processes if exposed to high levels of moisture or low levels of moisture for significant periods of time.
Conventional capacitors such as those used for aerospace, industrial, and automotive applications commonly utilize either a plastic or metal case which surrounds the actual capacitive element to provide moisture protection for applications where moisture protection is required. However, the plastic and metal cases used for this purpose may exhibit inadequate moisture protection and add significantly to the cost, size and weight of these conventional capacitors.
Complete electronic units such as a circuit board may be sealed against moisture by structural design or through the application of a coating to the entire electronic unit. These designs, coatings, and related processes, however, may interfere with cooling airflow, repair and maintenance activity, and other operational requirements. Additionally, the designs and coating may increase the cost, size, and/or weight of the electronic unit.
Accordingly, a compact, lightweight, and inexpensive capacitor that provides resistance to gas and moisture infiltration is needed.